MESON2021

Contribution ID: 66 Type: Plenary

Dark photon research and the X17 hypothetical particle Thursday, 20 May 2021 15:45 (30 minutes)

Dark Matter is currently one of the greatest unsolved mysteries in physics. Our current knowledge isencom- passed in the Standard Model (SM) of particle physics. While the SM is phenomenally successful in describing the physics of familiar matter to high precision, it is also known to be incomplete. In particular, newphysics must be responsible for the dark matter. This discovery triggered an enormous theoretical and experimental interest in the particle and hadron physics community. The theoretically predicted hypothetical Dark Photon particles does not serve as the Dark Matter particleit- self, but acts as a messenger particle of a hypothetical Dark Sector with residual interaction to the Standard Model. Dark Photons are of an extra U(1) gauge group. Such extra U(1) gauge groups are predicted by almost any extension of the Standard Model. Indeed, the related extra U(1) gauge bosons are searched for from the lowest energies up to the highest ones. Recently, the mass range for a vector particle in the MeV to GeV scale has been in the focus, since such a mass scale might explain a surprisingly large number of astrophysical and other anomalies. Recently, we observed a peak-like enhancement relative to the internal pair creation at 140° in the angular correlation of the e+e- pairs created in the 18.15 MeV ground state transition of 8Be [1]. It turned out that this could be a first hint for a new mxc2=17 MeV boson, called X17 in the literature. The data are explained by Feng et al. [2] with a 16.7 MeV, Jπ= 1- vector gauge boson, which may mediatethe fifth force with some coupling to SM particles. Ellwanger and Moretti made another possible explanationof the experimental results through a light pseudo scalar, Jπ= 0- particle [3], while Kozaczuk et al., [4] explained it as an axial vector, Jπ= 1+ boson. There are also many more possible explanations in the literature. Using a significantly modified and improved detector setup, we reinvestigated the anomaly observed inthe e+e- angular correlation by using a new Tandetron accelerator of our institute and the previous data were reproduced within the error bars. We also studied the 3H(p,γ)4He reaction (Q=20.6 MeV) at three different proton energies (Ep=510, 610 and 900 keV) and observed e+e- pairs with a smooth angular correlation, but on top of that a peak at Θ≈115° is clearly visible at each proton energies with larger than 7σ confidence, which can be described by assuming the creation and decay of the same X17 boson [5] as observed previously in 8Be.. References: [1] A.J. Krasznahorkay et al., Phys. Rev. Lett. 116 042501 (2016). [2] J. Feng et al., Phys. Rev. Lett. 1 17, 071803 (2016) . [3] Dark Sectors 2016 Workshop: Community Report [4] Ulrich Ellwanger and Stefano Moretti, JHEP 11, 039 (2016). [5] Jonathan Kozaczuk, et al., Phys. Rev. D 95, 115024 (2017). [5] A.J. Krasznahorkay et al., J. Phys.: Conf. Ser. 1643, 012001 (2020).

Collaboration ATOMKI

Primary author: KRASZNAHORKAY, Attila (Institute for Nuclear Research (ATOMKI)) Presenter: KRASZNAHORKAY, Attila (Institute for Nuclear Research (ATOMKI)) Session Classification: Plenary Session